//快速幂
let x = 2.00000, n = 10
var myPow = function(x, n) {
    let ans =1
    if(x<0){
        let x = 1/x
        n=-n
    }
    while(n){
        if(n%2){
            ans = ans*x
        }
        x*=x
        n = Math.floor(n/2)
    }
    return ans
};